That model always had the tacit agreement that the company releases early, and the users accept that they are part of a large testing base with one or two major updates to come. Further to this, continued support in the early life drives more sales. There’s a spectrum of users from bleeding edge to 4 versions behind. Some will hold out and never upgrade if key bugs remain, so updates make business sense. Software of this complexity has to be this way to strike a balance to move new features forward.

Because it’s beneficial for the software company’s reputation. People are more likely to buy the software when they know that it’s not going to get a permanently unpatched zero-day the moment the next version comes out.

In this day and age people expect security and operational patches. It’s hard work maintaining software, even if it is feature complete.